In modern communications technology it has become common practice to provide two related but separate network infrastructures: a transmission network for carrying enduser data traffic, and a signalling network for controlling operation of the transmission network in accordance with control signals transferred through the signalling network. In practice such signalling networks comprise high-speed computers interconnected by signalling links; computer programs control the computers to provide a set of operational and signalling functions in accordance with a standardized protocol. One example of such a signalling protocol is the afore-mentionned Signalling System No. 7 (SS7) which is being extensively deployed for control of telephone and other data transmission networks. An SS7 network basically comprises various types of signalling points, namely, signalling end points (SEPs) and signalling transfer points (STPs) interconnected by signalling links, the SEPs being associated for example with respective service switching points (SSPs) of the transmission network, and service control points (SCPs). Congestion may arise in the signalling network as a result, for example, of a number
of SEPs simultaneously wishing to pass messages to another SEP (such as an SCP providing a database resource to the network). In this case, the links to the target SEP may not be able to handle the concentration of message traffic. To manage such possible congestion, the SS7 protocol provides a congestion control mechanism by which when a message is received in the outgoing buffer of a link causing the buffer to be filled to an upper-threshold level, a choking message is sent back to the SEP that generated the message, temporarily requiring it not to send any more messages to the same destination. When the buffer level falls below a lower threshold, the link is taken as no longer congested. This congestion control mechanism is primarily operated in the signalling transfer points.
A drawback with such a congestion control mechanism is that it is non-selective in nature--once congestion occurs in a link, choking messages are issued in response to all subsequently received messages until the link becomes non-congested, regardless of the origin, destination or content of the messages.
One possible way of reducing congestion would be to introduce a selective restriction mechanism in each existing signalling point that restricted the flow of certain predetermined types of messages, such as messages originating from a particular signalling point or concerning a particular called party. Such a mechanism would, for example, prevent more than a given number of messages from an originating signalling point from passing through a particular network node in unit time. A drawback of this mechanism is that it requires analysis of the messages and this causes processing overhead in the signalling points. Such overhead is particularly undesirable where the existing signalling point is a network resource such as an SCP because it is such resources that are the likely bottlenecks in the system.
Indeed, it would be useful generally to reduce the processing load of signalling points such as SCP, as this would enable them to handle more messages per unit time and improve overall network performance.
It is therefore an object of the present invention to provide a selective message restriction apparatus that does not require processing overhead in the existing signalling points. A separate objective of the present invention is to provide apparatus that can remove certain processing tasks from the existing network signalling points, particularly signalling end points.